For ease of description, we shall refer to such a spray nozzle assembly in terms of one associated with spray drying of milk.
In general spray nozzles which are provided with swirl chambers and orifice discs have these components manufactured from tungsten carbide or the like which is very hard but also brittle and prone to damage when dropped or other wise roughly treated during assembly and disassembly.
When ordinary spray nozzles are used for spray drying milk a certain percentage of the liquid simply fell as drops from the nozzles, without being atomized, and this material could well lead to pollution of the product.
To avoid this problem a unitary check valve was developed for spray drying nozzles, and other nozzles, which caused little restriction in the flow through the nozzle and which, at the same time, did not have any parts likely to be passed into the fluid stream.
Conventional check valves however have sealing problems when operated at high pressures and are not necessarily as compact as would be desirable.